<!DOCTYPE html>
<html>
<head>
    <meta charset='utf-8' />
    <title>Add hillshading</title>
    <meta name='viewport' content='initial-scale=1,maximum-scale=1,user-scalable=no' />
    <script src='https://api.tiles.mapbox.com/mapbox-gl-js/v0.46.0/mapbox-gl.js'></script>
    <link href='https://api.tiles.mapbox.com/mapbox-gl-js/v0.46.0/mapbox-gl.css' rel='stylesheet' />
    <style>
        body { margin:0; padding:0; }
        #map { position:absolute; top:0; bottom:0; width:100%; }
    </style>
</head>
<body>

<div id='map'></div>
<script>
mapboxgl.accessToken = 'pk.eyJ1IjoieWFuY29uZ3dlbiIsImEiOiJjaml4eWgxMnowNHY0M3BvMW96cDI1bWJ6In0.QA-bmCCquo-mziBfZ8KOIQ';
var map = new mapboxgl.Map({
    container: 'map',
    style: 'mapbox://styles/mapbox/cjaudgl840gn32rnrepcb9b9g', // the outdoors-v10 style but without Hillshade layers
    center: [-119.5591, 37.715],
    zoom: 9
});

map.on('load', function () {
    map.addSource('dem', {
        "type": "raster-dem",
        "url": "mapbox://mapbox.terrain-rgb"
    });
    map.addLayer({
        "id": "hillshading",
        "source": "dem",
        "type": "hillshade"
    // insert below waterway-river-canal-shadow;
    // where hillshading sits in the Mapbox Outdoors style
    }, 'waterway-river-canal-shadow');
});
</script>

</body>
</html>